The present invention relates to a coil apparatus such as gradient magnetic field coil apparatus of magnetic resonance imaging apparatus, and a method of manufacturing the same.
This application is based on Japanese Patent Application No. 10-186463, filed Jul. 1, 1998, the content of which is incorporated herein by reference.
In a magnetic resonance imaging apparatus, a gradient magnetic field coil is located inside of a magnet (super-conductive magnet, ordinary conductive magnet, permanent magnet) for generating a static magnetic field. The gradient magnetic field coil is usually composed of three sets of coils called Gx, Gy, Gz coils, and a gradient magnetic field differing in the intensity linearly in each orthogonal direction of x-, y-, and z-axes. Herein, usually, the z-axis direction is the axial direction of the object, and the lateral direction (width direction) of the object is the x-axis direction, and the depth direction (thickness direction) of the object is the y-axis direction.
The gradient magnetic field has a linear inclination in the static magnetic field (principal magnetic field) for the purpose of arbitrarily determining the imaging section, or adding the position information to the RF signal from the object. A required performance of the gradient magnetic field coil includes the linearity of the gradient magnetic field in order to give accurate position information. The shape of the gradient magnetic field coil differs with the direction of the static magnetic field, and direction of inclination, but usually a pair of loop coils are used as Gz coil, and four saddle coil sets are generally used as Gx and Gy coils. Actually, moreover, outside of the gradient magnetic field coil, a shield coil of substantially the same shape is provided in order to prevent leak of magnetic field from the gradient magnetic field coil to outside.
The shape of the saddle coil is part of the surface of columnar or elliptical columnar form, and hence it is hard to manufacture. In a conventional manufacturing method of saddle coil, a coil winding of a specified pattern is cutout from a flat conductor thin plate, an insulating sheet is adhered to the surface of the coil winding, and it is pressed against a pressing die to curve, thereby forming a saddle coil (for example, U.S. Pat. No. 5,349,744). As the coil winding cutting-out method, a wire cutter, laser, or water jet cutter may be used, or a method of blanking a thin plate to a die having the coil shape groove, or a method of etching may be employed.
In such conventional methods, commonly, since a coil winding is cut out from a flat conductor plate, and then curved, the manufacturing process is complicated, and it takes many days, but the manufacturing error cannot be prevented. Yet, the winding extending in the cylindrical direction of the cylinder is curved, but the winding extending in the axial direction of the cylinder is not curved. Accordingly, gradient magnetic field having linearity of high precision cannot be generated. Further, if a thick conductor plate is required, curling in peripheral direction may be formed in the process of curving the coil winding, and it is hard to process into a desired shape.
Thus, the conventional manufacturing method of gradient magnetic field coil (such as called saddle coil) is complicated in manufacturing process, long in manufacturing time, and not free from manufacturing error.